Products are sealed in packages for various reasons. These reasons include maintaining sterility of the products, preventing contact of the products with air preventing moisture loss or gain from the product, and for protection during shipping. For any one or more of these reasons, it may be desired to maintain a certain atmosphere within a sealed package. Therefore, opening these packages to determine product viability is not possible since the act of opening the package changes or destroys the desired atmosphere within the package.
To ensure that medical devices in particular are suitable for use, a destruction policy often requires discarding all devices over a certain age. This may be necessary due to the inability to determine the viability of a device inside a sealed package. Such a destruction policy may result in discarding and thereby wasting viable devices.
For example, defibrillation electrode pads may include several electrical connections and a hydrogel that facilitates their operation. The shelf life of electrode pads is determined in part by the length of time it takes for enough water moisture to evaporate out of the hydrogel and escape the pads package. As moisture escapes, the electrical properties of the electrode pads become increasingly compromised.
In one context, where electrode pads are utilized with a defibrillator, a very significant factor includes changes in small and large signal impedance values between a patient's skin and the defibrillator. As the hydrogel dries out, the impedance values increase, making it more difficult to monitor a patient's electrical signals, obtain transthoracic impedance, and deliver energy into the body. Electrical continuity is compromised between the electrode and a patient's skin.
To help ensure that electrode pads will be usable when opened, electrode manufacturers currently print an expiration date on each set of pads. The electrode pads are to be discarded no later than the expiration date. However, the expiration date typically is determined based upon studies of the hydrogel used on the pads, and the amount of water moisture that escapes the package over time under normal as well as strenuous conditions. A safety factor is added to give time for the electrode pads to be shipped from the supplier to an original equipment manufacturer (OEM) and then from the OEM to the customer. This helps to ensure that the electrode pads are always usable, barring any package damage, when removed from the package before the expiration date.
Calculating the expiration date of electrode pads or other components as described above is a conservative method of ensuring quality. However, as a result, the expiration date may arrive before the pads have actually expired. In fact, electrode pads may be usable for much longer than the expiration date, especially if they are kept at room temperature or in a high humidity environment.
While electrode pads or other components may naturally over time become nonfunctional, at other times an electrode package may be damaged in some way. For example, tiny punctures or slits in the package, which may be too small to be seen by the casual observer or with the naked eye, or tears in the metal packaging layer caused by bonding the package, can allow water moisture to escape. Without noticing damage to the electrode pads' package, a customer typically will not replace electrode pads until the expiration date arrives, when in fact the pads may be unusable long before. In addition, an electrode may be bent or compressed inside its sealed package, thereby causing electrical discontinuities such as broken wires or connections.
The above example only represents one particular example of an electrode pad of a particular use. Electrode pads for other uses may be similarly affected. Also, devices other than electrode pads may be affected by age, storage, and package conditions. Furthermore, factors other than humidity can affect the functionality of a device.